Depending on bag length, tools (e.g., sealing jaws) typically used in such apparatus extend perpendicularly of the film feed direction and intermittently flatten and glue or weld the film tube, using heat and pressure to form the ends of the bags. To allow adequate time for the heated sealing jaws to act on the packaging material so that the film tube is sealed to form the bag ends, the sealing jaws must travel at the same speed as the film tube, and must return to the advancing film upstream by one bag length after each welding or gluing operation.
This return travel can be achieved through the known use of a mechanism in the form of paddle wheels having the sealing jaws mounted at the tips of the paddles. The paddle wheels rotate at such a rate that the travel (tangential) speed of the sealing jaws coincides with the film feed speed.
Another known arrangement for the return travel of the sealing jaws by one bag length after each welding operation consists of a mechanism which retracts the sealing jaws from the film through a cam arrangement or an articulated joint. The sealing jaws are then returned in a straight-line or orbital path to the position of the next welding line and from this point move synchronously with the film for the required sealing time.
The paddle wheel-type sealing mechanism significantly limits throughput speed because of the required contact (sealing) time of the sealing jaws, and because return of the sealing jaws upstream to the start position requires more time than the filling of a bag, thus requiring the film feed to be slowed or stopped. Similar problems exist with other types of known sealing mechanisms. If it is desired to increase the film feed speed for the same packaging material (which would require the same sealing time), it would be necessary to increase the length (stroke) of the sealing operation, which in turn would also prolong the time for return travel of the sealing jaws.